The present invention relates to a recording medium which makes record with ink and more particularly it relates to an ink jet recording sheet suitable as light transmission recording medium for overhead projector and the like.
According to ink jet recording method, droplets of ink are projected by various means and applied onto a recording medium to make record of images or letters thereon. This recording system has rapidly spread in various uses as hard copy devices for various figures and color images including Chinese characters because of high versatility for patterns to be recorded and easy multicolor recording. Especially, overhead projectors as well as slide projectors are widely utilized for many conferences, lectures, promotional meetings and the marketing of commercial goods and there are many advantages in preparation of recording medium for overhead projectors by ink jet recording method.
Hitherto, record medium for overhead projectors have been prepared by utilizing opacification of transparent film due to heat shrinkage, by reprography, by thermal transfer method or by direct writing on transparent film by felt pen and the like. When recording on these transparent films is attempted by ink jet recording method, since the recording surface of the films has no ink absorbency, aqueous ink requires a long time for drying or flows thereon and thus practically usable recorded images cannot be obtained. As an approach to promote apparent drying of recorded image, an ink jet recording medium comprising a transparent support and provided thereon a porous layer comprising more than 60% by weight of filler particles and a resin binder was proposed in Japanese Patent Unexamined Publication (Kokai) No. 57-14091. However, since the binder is a resin soluble in organic solvents and besides more than 60% by weight of filler is used, completely transparent layer cannot be produced and thus the medium can be used for diazotype second original, but is unsatisfactory for overhead projectors.
When transparency is required as in recording sheets for overhead projectors, inorganic pigments cannot be used in a large amount and it is necessary to absorb and fix the ink with high molecular weight material alone.
With reference to the use of high molecular weight materials, there are disclosed, for example, polyvinyl pyrrolidone or polyvinyl pyrrolidone-vinyl acetate copolymer in Japanese Patent Unexamined Publication (Kokai) No. 57-38185, absorbing resins in Japanese Patent Unexamined Publication (Kokai) No. 57-17319, polymers having both the hydrophilic portion and hydrophobic portion in Japanese Patent Unexamined Publication (Kokai) No. 58-134784, copolymers of PVA and olefin or styrene and maleic anhydride in Japanese Patent Unexamined Publication (Kokai) No. 60-234879, use of two-layer structure consisting of ink-retention layer and ink-permeable layer, in Japanese Patent Unexamined Publication (Kokai) No. 6135276, use of crosslinked layer of ethylene oxide polymer with isocyanate compound in Japanese Patent Unexamined Publication (Kokai) No. 61-74879, use of materials comprising combination of carboxy-containing polymer and hydrophilic resin in Japanese Patent Unexamined Publication (Kokai) No. 61-102286, cationized PVA in Japanese Patent Unexamined Publication (Kokai) No. 61-272796, use of polyvinyl pyrrolidone having an average molecular weight of at least 100,000 in Japanese Patent Unexamined Publication (Kokai) No. 61-32788, use of an ink absorbing layer of a specific water-soluble resin and provided thereon a non-tacky water-soluble high molecular substance in Japanese Patent Unexamined Publication (Kokai) No. 61125878, use of a blend of carboxymethyl cellulose and polyethylene oxide in Japanese Patent Unexamined Publication (Kokai) No. 61-181679, use of modified PA having silyl group in Japanese Patent Unexamined Publication (Kokai) No. 61-134290 and use of graft polymer of methacrylamide on polyvinyl alcohol in Japanese Patent Unexamined Publication (Kokai) No. 61-132377.
As mentioned above, ink jet recording media are required to have properties such as absorbency of ink, especially aqueous ink and drying characteristics. Furthermore, for overhead projectors, the recording media are required to be superior in light transmission of support and ink-receiving layer. However, there have been provided no satisfactory recording media by the conventional high molecular weight materials and techniques.